Small Craft Advisory 287, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT SUN MAR 30 2008

.MODEL DISCUSSION AND UPPER LEVELS...
OPERATIONAL 12Z ECMWF AND GFS IN GOOD AGREEMENT THROUGH FRIDAY
MORNING. BOTH MODELS HAVE A PROGRESSIVE TROUGH MOVING THROUGH THE
BERING SEA TONIGHT AND INTO THE EASTERN BERING TOMORROW NIGHT QUICKLY
FOLLOWED BY ANOTHER TROUGH. IN THE MEANTIME...A SHORT WAVE TROUGH TO
SWING THROUGH SOUTH CENTRAL ALASKA AND DISSIPATE AS THE MEAN RIDGE
AMPLIFIES OVER THE MAINLAND DUE TO THE BERING TROUGHS. THE FIRST
TROUGH TO SLOW DOWN AS IT HITS THE RIDGE TUESDAY AND THE FOLLOWING
TROUGH FEEDS INTO IT. THE COMBINATION OF THESE TWO WILL KNOCK DOWN
THE RIDGE IN THE GULF AND MAINLAND WEDNESDAY INTO THURSDAY. THIS
ALLOWS A DEEPER COLDER TROUGH TO SETTLER OVER 160-170W DEPENDING ON
THE MODEL CHOICE FRIDAY. THIS IS WHERE THE MODELS START TO DIFFER.
THE GFS IS STRONGER WITH AN UPPER LOW DEVELOPING OVER THE NORTHWEST
PACIFIC AND THEREFORE MAKES THE TROUGH NEAR 165W MORE PROGRESSIVE.
THE ECMWF THEREFORE LEAVE A STRONGER LOW IN THE BERING STRAIT AND A
MORE STAGNANT UPPER LEVEL PATTERN FOR SATURDAY AND SUNDAY. THE GFS
ENSEMBLE MEAN PLAYS THE SAME WAY BUT IS MUCH MORE BROAD WITH THE
SURFACE PRESSURE PATTERN AND SHORT WAVES MOVING ACROSS THE BERING
WEDNESDAY AND THURSDAY. MOST ENSEMBLE MEMBERS BEHAVING THIS WAY AS
WELL. JUST A PROBLEM IN THE DETAILS BETWEEN THE HIGHER RES
OPERATIONAL RUNS AND LOWER RES ENSEMBLES.

.ANALYSIS AND NEAR TERM FORECAST...
CURRENTLY...A LOW IS SITUATED ALONG THE WEST COAST OF ALASKA WITH A
FRONT MOVING UP THE WESTERN GULF. PLENTY OF PRECIPITATION ACROSS
SOUTHWEST ALASKA. THE PRECIPITATION WILL SWING WEST OVERNIGHT AS THE
UPPER LEVEL SHORT WAVE PASSES ACROSS THE MAINLAND. PRECIPITATION WILL
DIMINISH FROM THE WEST MONDAY. SNOW ADVISORY BEEN ISSUED FOR THE
NORTHERN SUSITNA VALLEY. THOUGHT OF SAME SCENARIO IN THE KUSKOKWIM
VALLEY. AFTERNOON PACKAGE WILL GO WITH THIS FOR TONIGHT AS THE TEMPS
NOT CONTINUING TO WARM THAT MUCH IN THE NORTHERN PORTION OF THE KUSKO
VALLEY. THE SOUTHERN EDGE OF THE KUSKOKWIM VALLEY WILL LIKELY BE A
RAIN/SNOW MIX FOR MUCH OF THE EVENING. AREAS OF FOG BEHIND THE FRONT
ALONG THE COAST AS WINDS HAVE DIMINISHED. THESE FOG CONDITIONS TO
LAST OVERNIGHT BEFORE WINDS PICK UP FROM A LOW MOVING ACROSS THE
BERING TONIGHT WHICH IS CURRENTLY OVER THE WESTERN ALEUTIANS. THE
FRONT ALONG THE WEST COAST CURRENTLY OVER KODIAK AND MOVING UP THE
KENAI PENINSULA.

.SHORT TERM FORECAST...
BERING AND ALEUTIANS...
LOW PRESSURE SYSTEM CURRENTLY OVER THE WESTERN ALEUTIANS. THIS SYSTEM
TO WRAP MORE WARM AIR INTO THE BERING TONIGHT AND TOMORROW. THE LOW
MOVES PAST ST MATTHEW ISLAND TOMORROW AFTERNOON AND INTO THE ARCTIC
TUESDAY NIGHT. COLD AIR WRAPS AROUND THIS LOW AND PROVIDES SOME
STRONGER GALE FORCE WINDS. IT ALSO WILL CHANGE RAIN TO SNOW SHOWERS.
HIGH PRESSURE BRIEFLY MOVES FROM THE WESTERN BERING INTO THE CENTRAL
BERING TUESDAY AFTERNOON INTO WEDNESDAY MORNING. A LOW WILL MOVE TO
THE WESTERN BERING WEDNESDAY MORNING WITH SOME WARM ADVECTION AND
GREAT JET SUPPORT. WILL POSSIBLY SEE SOME STRONG WINDS WITH THIS LOW
AND ASSOCIATED FRONT.

WESTERN ALASKA...
A LOW ALONG THE COAST WITH GOOD SOUTHERLY MOISTURE FLOW INTO THE
MAINLAND. THIS SCENARIO PRODUCING PLENTY OF PRECIPITATION FOR
SOUTHWEST ALASKA. RAIN MIXED WITH SNOW IN THE YK DELTA AND BRISTOL
BAY AREA. RAIN AND SNOW MIX EVEN INTO THE SOUTHERN KUSKO VALLEY. THE
PRECIP SHOULD STAY ALL SNOW IN THE NORTHERN VALLEY. AS THE LOW LIFTS
ACROSS THE AREA TONIGHT AND TOMORROW PRECIP TO DIMINISH BY NOON
TOMORROW. ANOTHER LOW MOVES INTO THE CENTRAL BERING TOMORROW KICKING
UP WINDS ALONG THE COAST AND RIDDING THEM OF FOG THAT IS CURRENTLY
THERE. THE FRONT MOVES INLAND MONDAY NIGHT BRINGING ANOTHER ROUND OF
PRECIPITATION TO WESTERN ALASKA. THE AIR MASS WILL BE EVEN WARMER FOR
THIS ROUND AND EXPECT MOSTLY RAIN WITH A RAIN SNOW MIX IN THE KUSKO
VALLEY. THIS SYSTEM MOVES OUT OF THE AREA TUESDAY BUT SHOWERS WILL
REMAIN THROUGH WEDNESDAY. THE SHOWERS WILL TURN TO SNOW AS COLD AIR
WRAPS BEHIND THE LOW.

SOUTH CENTRAL...
A FRONT MOVING UP THE WESTERN GULF TONIGHT WITH THE LOW BACK NEAR THE
YK DELTA. THIS IS PROVIDING A GOOD EAST WEST GRADIENT ALONG THE
NORTHERN GULF COAST. PRECIPITATION MAINLY IN A DOWNSLOPE PATTERN AS A
GOOD EAST WEST PRESSURE GRADIENT ALONG THE NORTHERN GULF COAST. THE
GAP WINDS WILL DIMINISH A SHORT TIME TOMORROW MORNING BEFORE
RE-ESTABLISHING TOMORROW AFTERNOON. THE BRIEF RESPITE WILL ALLOW SOME
PRECIPITATION TO WORK INTO THE DOWNSLOPE DRY AREAS FOR A TIME.
PRECIPITATION TO WANE FROM THE WEST MONDAY BEFORE A NEW FRONT MOVES
INTO THE WESTERN GULF MONDAY NIGHT AND UP TO THE NORTHERN COAST BY
TUESDAY MORNING. SOUTH CENTRAL WILL GO THROUGH THE SAME SCENE AS
TODAY AND TONIGHT FOR TUESDAY NIGHT. HOWEVER...THIS AIR MASS WILL BE
WARMER WITH MORE AREAS OF RAIN THAN SNOW. PRECIP WILL DIMINISH FROM
DURING THE DAY WEDNESDAY.

.LONG TERM FORECAST...
IN GENERAL...A LOW WRAPS UP IN THE BERING THURSDAY AND PROGRESSES
INTO THE MAINLAND WITH A SURFACE TROUGH ACROSS THE GULF FRIDAY.
PRECIPITATION TO BE A MIX AT FIRST BUT BEHIND THE LOW PRECIP WILL
TURN TO ALL SNOW BEFORE IT ENDS FROM THE WEST SATURDAY ALONG THE WEST
COAST AND THROUGH THE MAINLAND SUNDAY. ANOTHER LOW TO PUSH ACROSS THE
ALEUTIANS SATURDAY AND SUNDAY WITH ANOTHER EPISODE OF WARM ADVECTION
AND RAIN AND CHANGING TO SNOW ON THE BACK SIDE. THE LOW WORKS INTO
THE GULF SUNDAY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...SNOW ADVISORY ZONES 145 AND 151
MARINE...GALE 155 172 175 176
FIRE WEATHER...NONE

JN MAR 08